Two people are in hospital, but recovering, after three confirmed cases of measles in the region on Tuesday. A fourth person has now been infected.

A fourth case of measles has been confirmed in Canterbury.

A teenager from Rangiora in North Canterbury is the latest person to contract the disease. The case was confirmed on Wednesday by the Canterbury District Health Board (CDHB).

Health authorities on Tuesday confirmed three people in Rangiora and Christchurch had contracted measles: a teenager and a man and a woman in their 40s.

People are considered immune from measles if they have had two doses of measles, mumps, rubella (MMR) vaccine, have had the disease before, or were born before 1969. (File photo)ANDY JACKSON/STUFF

People are considered immune from measles if they have had two doses of measles, mumps, rubella (MMR) vaccine, have had the disease before, or were born before 1969.

None of the first group were thought to be fully immunised. People are considered immune if they have had two doses of measles, mumps, rubella (MMR) vaccine, have had the disease before, or were born before 1969.

* Three new cases of measles confirmed in Rangiora and Christchurch* University of Otago student contracts measles, prompting health warning* Six people in two Waikato households diagnosed with measles

It comes after an 18-year-old university student in Dunedin was confirmed to have measles on Friday. The woman was not thought to be immunised, health authorities said.

It was possible people may not know if they are fully protected against measles, health officials say.

University of Auckland associate professor Nikki Turner, director of the Immunisation Advisory Committee, said historical vaccination issues were a bigger problem for the spread of measles in New Zealand than current vaccine hesitation.

"We did not vaccinate very well 15 to 20 years ago for a whole lot of reasons. So it's a historical problem we've got," she said.

"If you look at the people getting measles, they're not young kids, because most of the young kids are protected."

Turner said it was possible people may not know if they were fully protected against measles. A centralised record-keeping system, the National Immunisation Register, was not rolled out until 2005.

The World Health Organisation (WHO) this year listed vaccine hesitation, the refusal or reluctance to vaccinate, as one of 10 threats to global health in 2019.

New Zealand is not exempt. Despite years of increasing immunisation coverage against various diseases, thousands of parents continue to decline at least one of the many vaccines freely available to children.

Dr Helen Petousis-Harris, a vaccinologist and senior lecturer at the University of Auckland, said declines in vaccine uptake globally were often closely followed by measles outbreaks.

"It's sort of like the canary in the mine. It's so super, super infectious that it's highly sensitive to declines in coverage," she said.

In 2017, New Zealand gained WHO-verification for successfully eliminating endemic measles and rubella for the first time, meaning no cases had originated in the country for the previous three years.

However, people who caught the disease overseas still regularly brought it back into the country.

The Ministry of Health publishes data showing the number of children who have received all their age-appropriate immunisations by each milestone age.

The vaccinations are detailed in the New Zealand immunisation schedule, which lists the series of freely offered vaccines to protect against various diseases.

Of the 63,413 children who turned 5 in 2018, 55,800, or 88 per cent were fully immunised for their age. The parents of 3160 children in the cohort had declined at least one of the available vaccines.

Petousis-Harris said there had always been some people sceptical of vaccines, but social media had changed the landscape. These groups were now better connected, and better able to spread misinformation, she said.

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